Sequential sputtering with movable targets



Nov. 3, 1970 L. F. HERTE ETAL SEQUENTIAL SPUTTERING WITH MOVABLE TARGETS Filed Sept. 15. 1967 ZSheets-Sheet 1 FIG. 5

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Nov. 3, 1970 L. F. HERTE ETAL 3,537,973

SEQUENTIAL SPUTTERING WITH MOVABLE TARGETS Filed Sept. 15, 1967 2 Sheets-Sheet 2 FIGJ WMJTZV I /////,i/ //J///////// I I l I c INVENTORS LAWRENCE F. HERTE RICHARD F. LAIB BY 3,. F W ATTORNEY United States Patent 3,537,973 SEQUENTIAL SPUTTERIN G WITH MOVABLE TARGETS Lawrence F. Herte, Palo Alto, and Richard F. Laib, Sunnyvale, Calif., assignors to Varian Associates, Palo Alto, Calif., a corporation of California Filed Sept. 15, 1967, Ser. No. 668,107 Int. Cl. C23c 15/00 US. Cl. 204-298 4 Claims ABSTRACT OF THE DISCLOSURE Sequential deposition of two or more layers of sputtered material is made.possible in sputtering apparatus employing peaked as well as plane parallel target electrodes by means of one or more movable, laminated, two layer targets. The two layer laminated target in which each layer is composed of different target material is pivotably supported on a shaft intermediate between two fixed target electrodes. In a first position, the laminated target is held against one of the fixed target electrodes exposing target material of a first composition for sputtering. After a predetermined time, the laminated target is positioned and held firmly against another of the fixed target electrodes exposing a second target material for sputtering. The targets are moved by a reversible drive motor which is mechanically coupled to a shaft supporting the laminated targets. The drive motor is provided with a holding circuit for firmly holding the laminated targets in position during sputtering.

BACKGROUND OF THE INVENTION The present invention is related in general to cathodic sputtering apparatus. In particular, it is directed to sequential sputtering apparatus for use in making laminated thin films and as such represents an improvement over such prior known sputtering apparatus as are disclosed in copending United States application Ser. No. 625,733, filed Mar. 24, 1967 and application Ser. No. 662,637, filed Aug. 23, 1967, and both assigned to the assignee of the present invention.

In application Ser. No. 625,733 there is disclosed sputtering apparatus employing two planar target electrodes disposed at an angle relative to one another in such a manner as to form a peak or roof over the adjacent substrates. In application Ser. No. 662,637 there is disclosed sputtering apparatus employing two plane parallel target electrodes disposed horizontally relative to the adjacent substrates.

In copending US. application Ser. No. 674,539, filed Oct. 11, 1967 and assigned to the assignee of the present invention there is disclosed sequential sputtering apparatus employing a novel shield and substrate holder; however, as in the first two mentioned cases, the target electrodes and targets are rigidly fixed and immovable during any single sputtering cycle.

To the extent that means are provided in the present invention to position targets of various sputtering material for sputtering during a single sputtering cycle, the present invention is an improvement over the above referred to inventions and prior known conventional sputtering apparatus all of which employ fixed immovable targets.

Patented Nov. 3, 1970 SUMMARY OF THE INVENTION In contrast to prior known sputtering apparatus in which both the targets and target electrodes are held in a fixed position throughout a sputtering operation, the present invention permits repositioning of targets at intermediate stages in order to facilitate the making of laminated thin films rapidly, for less cost and without defects caused by atmospheric contamination.

As more fully described hereinafter, a movable laminated target consisting of two layers of different target material is supported intermediate two fixed target electrodes. In one position of the laminated target, target material on one of the fixed target electrodes and one layer of the laminated target is exposed to the substrates for sputtering material. In a second position of the laminated target, target material on the second of the fixed targets and on the opposing layer of the laminated target is presented to the substrates. As a consequence, laminated thin films of difiFerent materials can be produced during a single sputtering operation or pump down cycle.

In terms of specific apparatus embodying the invention, a reversible motor is mechanically coupled to a rotatable shaft supporting the laminated target for pivoting the laminated target to either of two sputtering stations. The motor may be, for example, an S550 Slosyn motor. In operation, 60 cycle power is applied to the motor to drive the laminated target to the desired position after which a small DC. voltage is applied to hold the target in position. Alternatively, over-the-center latches may be afiixed to the surrounding shield to catch and hold the laminated target in position. Since efiicient sputtering demands as low a residual gas pressure as possible in terms of both high rates as well as purity of film deposition, it is becoming more and more imperative that all sputtering operations on any single substrate be performed during a single pump down cycle. This is particularly true where the thin film devices are intended for use in research as well as commercially produced cryogenic and microminiature electronic circuits.

While operational plasma pressures may be considerably higher during sputtering, certain applications requiring extremely well controlled atmosphere establish initial sputtering conditions which necessitate pumping vacuums to pressures as low as 10- torr. Vacuum pumping of that nature with presently existing equipment exceeds elapsed times of 30 minutes.

Accordingly, a primary object of the present invention is sputtering apparatus for making thin films more effi ciently, at less cost and without atmospheric contamination during intermediate stages of processing.

Another object of the invention is sputtering apparatus for making laminated thin films by means of a movable laminated, two layer target.

Another object of the invention is sputtering apparatus as described in which the laminated target is driven by an externally controlled reversible motor.

These and other objects, features and advantages of the invention will become apparent from the detailed description hereinafter when considered together with the accompanying drawings in which:

FIG. 1 is a front elevational view of a sputtering system embodying the present invention,

FIG. 2 is an enlarged view of the sputtering head of FIG. 1,

3 FIG. 3 is a side view of the sputtering head as shown in FIG. 2, and

FIGS. 4 and are alternative sputtering heads embodying the present invention.

DETAILED DESCRIPTION In FIG. 1 there is shown a sputtering module 1 including a pair of adjacent target electrodes 2, 3 and a substrate holder 4 supported Within a vacuum chamber 5 by means of two brackets 6, 7 adjustably attached to a vertically rising stainless steel pipe 8. The provision for adjusting brackets 6, 7 along the length of pipe 8 is for setting the target to substrate distance, which is a primary factor in obtaining optimum rates of sputtering and deposition.

Vacuum chamber 5 in which sputtering module 1 is enclosed is formed by a vacuum envelope 15, such as a bell jar, seated in a vacuum tight manner on a stainless steel spool-type vacuum manifold 16. A high vacuum pump system 17 is connected to manifold 16 in a vacuum type manner for evaculating chamber 5 of residual gas to a pressure as low as torr. Provision is made also in pump system 17 for back filling vacuum chamber 5 with an inert chemically pure gas, such as argon, from which a glow discharge is generated and maintained during sputtering. The reduction of residual gas and back filling with an inert gas insures there is sufiicient ionization for efficient sputtering and at the same time avoids contamination and deterioration of the thin film and substrates due to chemical reaction with gases which may be present in air.

Pipe 8 connected to the upper section of sputtering module 1 together with a pipe 18 connected to the substrate holder 4 provide conduit for fluid cooling lines used in cooling electrodes 2, 3 and substrate holder 4. A pair of cooling tubes 20, 21 running to the electrodes 2, 3 may be made of either dielectric or conductive material. When made of conductive material they may function as transmission lines for electrical energy for electrodes 2, 3. In addition to functioning as conduit for cooling fluids and electrical energy to electrodes 2, 3, tubes 20, 21 may be mechanically fixed to the upper surface of electrodes 2, 3, rs by brazing, and serve to mechanically support electrodes 2, 3 in a peaked configuration as shown in FIG. 1 or in a plane parallel configuration as shown at 2', 3' in FIG. 4.

Target material 24, 25 is affixed to the lower surfaces of electrodes 2, 3 in any well known manner, as by clips (not shown). In operation, ions from the glow discharge formed in the space between electrodes 2, 3 and substrate holder 4 are accelerated to electrodes 2, 3 and upon impact with target material 24, 25 eject mostly neutral particles of target material which then deposits on and ad heres to substrates 26 supported on substrate holder 4. Target 24 is made of one material and target 25 is made of a different material.

To produce laminated thin films on substrates 26, a third target 27 is pivotably disposed between electrodes 2, 3. Target 27 has laminae of target material of differing composition on opposed surfaces. One lamina of target 27 is identical to the target material 24 aflixed to electrode 2. The other lamina 31 of target 27 is identical to the target material 25 afiixed to electrode 3. When positioned for sputtering, target 27 and one of the targets afiixed to electrodes 2, 3 thus present identical sputtering material to substrates 26 for sputtering.

Referring to FIG. 2, there is shown the upper section of sputtering module 1. Electrodes 2, 3 supported by tubes 20, 21 are held in a fixed position relative to substrate holder 4. Three brackets 28 for supporting laminated target 27 are attached to a grounded shield 29 intermediate electrodes 2, 3. The lower ends of brackets 28 are formed to accept a shaft 34. Laminated target 27 is attached to shaft 34 at intermediate points along the length of shaft 34 by two laminated target retaining collars 35.

Fasteners 39, such as pins or screws, hold the laminated target 27 within collar 35 and permit easy interchange of laminated target 27 with laminated targets of different composition.

Referring to FIG. 3, a vacuum compatible reversible motor 38, such as an SSSO Slosyn motor, is coupled to the end of shaft 34. Shaft supporting brackets 28 for supporting shaft 34 are positioned near the ends and center of shaft 34. Target retaining collars 35 are pos1- tioned intermediate brackets 28.

In operation, target 27 is driven by motor 38 to a position abutting either target 24 or 25 and is held in place by application of a small D.C. holding voltage to motor 38. Alternatively, over-the-center latches may be fixed to a shield 29 for catching and holding target 27. As shown in solid lines in FIG. 2, target 27 is abutting target 24, thereby blocking sputtering from such target and positioning material 31 in its place for sputtering. In the illustrated solid line position, target material 3 1 of target 27, and target material 25 afiixed to electrode 3, are exposed for sputtering. In a second position (shown in dotdash lines) of the target 27 in which it abuts target material 25, it blocks sputtering from such material and target material 30 of target 27 and target material 24 affixed to electrode 2 would be exposed for sputtering. Thus, in accordance with the invention as described, laminated thin films of different compositions can be produced without bringing the vacuum chamber up to air to change target material.

As will be apparent to those skilled in the art, the target material on each of target 27 and electrodes 2, 3 exposed for sputtering need not be the same. Differing target material would permit deposition of composite thin films. Similarly, the invention is not limited to a single laminated pivotable target but encompasses plural lam inated targets which may be selectively positioned by appropriate controls.

An alternative embodiment similar to that described above is shown in FIG. 4 wherein modified parts are identified with primed reference numbers. In FIG. 4 electrodes 2', 3' are positioned in parallel planes.

A third alternative, as shown in FIG. 5, is similar to both the peaked and plane parallel electrode configurations above described. It consists of a single target electrode 2" with a movable target 27", shaft 34" and drive motor (not shown) positioned at one end of the target electrode.

Since movable target 27" is moved only into a single sputtering position, it is not necessary that it be laminated; however, it will be readily seen that laminated targets could be used though one side, the side nearest the target electrode 2", would be ineffective.

Other embodiments and alternative features will be obvious to those skilled in the art. Accordingly, the described embodiments shall be considered as illustrative only and in no way limiting the scope of the invention.

What is claimed is:

1. Sputtering apparatus for depositing films of different materials on substrates, said apparatus comprising at least two target electrodes, each of which is adapted to hold a target material on a surface for sputtering by ionic bombardment of particles of the material therefrom; a substrate holder spaced from said surfaces of said target electrodes for holding substrates to be coated in position for deposition of material sputtered from said electrodes; and a movable target assembly being pivotally mounted within said apparatus having means to hold target material on each of two opposed surfaces thereof, said target assembly being pivotable between a first position blocking sputtering from a first one of said target electrodes and presenting in its place for sputtering a first one of said two opposed surfaces, and a second position blocking sputtering from the other one of said target electrodes and presenting in its place for sputtering the other one of said two opposed surfaces.

2. The sputtering apparatus of claim 1 wherein said surfaces of said target electrodes are adjacent one another and said target assembly is pivotally mounted therebetween for said movement between said first and second positions, and drive means is coupled to said target assembly for selectively pivoting the same between said positions.

3. Apparatus according to claim 2 including a shaft between said target electrodes, said movable target assembly being attached to said shaft, said shaft being coupled to said drive means, and said drive means being an electric motor.

4. Apparatus according to claim 4 wherein said target assembly is held in either selected one of said first or see- 0nd positions by the application of a low D.C. voltage to said motor.

References Cited UNITED STATES PATENTS 3,418,229 12/1968 Lakshmanan et a1. 204--298 JOHN H. MACK, Primary Examiner S. S. KANTER, Assistant Examiner 

